Package org.apache.commons.math.linear

Class OpenMapRealVector

java.lang.Object

org.apache.commons.math.linear.AbstractRealVector

org.apache.commons.math.linear.OpenMapRealVector

All Implemented Interfaces:

Serializable, RealVector, SparseRealVector

public class OpenMapRealVector
extends AbstractRealVector
implements SparseRealVector, Serializable

This class implements the RealVector interface with a OpenIntToDoubleHashMap backing store.

Since:

2.0

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.commons.math.linear.RealVector

RealVector.Entry

Field Summary

Fields

Modifier and Type	Field	Description
static final double	DEFAULT_ZERO_TOLERANCE	Default Tolerance for having a value considered zero.

Constructor Summary

Constructors

Constructor	Description
OpenMapRealVector()	Build a 0-length vector.
OpenMapRealVector(double[] values)	Create from a double array.
OpenMapRealVector(double[] values, double epsilon)	Create from a double array, specifying zero tolerance.
OpenMapRealVector(int dimension)	Construct a (dimension)-length vector of zeros.
OpenMapRealVector(int dimension, double epsilon)	Construct a (dimension)-length vector of zeros, specifying zero tolerance.
OpenMapRealVector(int dimension, int expectedSize)	Build a vector with known the sparseness (for advanced use only).
OpenMapRealVector(int dimension, int expectedSize, double epsilon)	Build a vector with known the sparseness and zero tolerance setting (for advanced use only).
OpenMapRealVector(Double[] values)	Create from a Double array.
OpenMapRealVector(Double[] values, double epsilon)	Create from a Double array.
OpenMapRealVector(OpenMapRealVector v)	Copy constructor.
OpenMapRealVector(RealVector v)	Generic copy constructor.

Method Summary

Modifier and Type	Method	Description
OpenMapRealVector	add(OpenMapRealVector v)	Optimized method to add two OpenMapRealVectors.
RealVector	add(RealVector v)	Compute the sum of this vector and v.
OpenMapRealVector	append(double d)	Construct a vector by appending a double to this vector.
OpenMapRealVector	append(double[] a)	Construct a vector by appending a double array to this vector.
OpenMapRealVector	append(OpenMapRealVector v)	Optimized method to append a OpenMapRealVector.
OpenMapRealVector	append(RealVector v)	Construct a vector by appending a vector to this vector.
OpenMapRealVector	copy()	Returns a (deep) copy of this vector.
double	dotProduct(OpenMapRealVector v)	Optimized method to compute the dot product with an OpenMapRealVector.
double	dotProduct(RealVector v)	Compute the dot product.
OpenMapRealVector	ebeDivide(double[] v)	Element-by-element division.
OpenMapRealVector	ebeDivide(RealVector v)	Element-by-element division.
OpenMapRealVector	ebeMultiply(double[] v)	Element-by-element multiplication.
OpenMapRealVector	ebeMultiply(RealVector v)	Element-by-element multiplication.
boolean	equals(Object obj)	Implementation Note: This performs an exact comparison, and as a result it is possible for a.subtract(b} to be the zero vector, while a.equals(b) == false.
double[]	getData()	Returns vector entries as a double array.
int	getDimension()	Returns the size of the vector.
double	getDistance(double[] v)	Distance between two vectors.
double	getDistance(OpenMapRealVector v)	Optimized method to compute distance.
double	getDistance(RealVector v)	Distance between two vectors.
double	getEntry(int index)	Returns the entry in the specified index.
double	getL1Distance(double[] v)	Distance between two vectors.
double	getL1Distance(OpenMapRealVector v)	Distance between two vectors.
double	getL1Distance(RealVector v)	Distance between two vectors.
double	getLInfDistance(double[] v)	Distance between two vectors.
double	getLInfDistance(RealVector v)	Distance between two vectors.
double	getSparcity()	Deprecated. as of 2.2 replaced by the correctly spelled getSparsity()
double	getSparsity()
OpenMapRealVector	getSubVector(int index, int n)	Get a subvector from consecutive elements.
int	hashCode()
boolean	isInfinite()	Check whether any coordinate of this vector is infinite and none are NaN.
boolean	isNaN()	Check whether any coordinate of this vector is NaN.
OpenMapRealVector	mapAdd(double d)	Add a value to each entry.
OpenMapRealVector	mapAddToSelf(double d)	Add a value to each entry.
RealMatrix	outerProduct(double[] v)	Compute the outer product.
OpenMapRealVector	projection(double[] v)	Find the orthogonal projection of this vector onto another vector.
RealVector	projection(RealVector v)	Find the orthogonal projection of this vector onto another vector.
void	set(double value)	Set all elements to a single value.
void	setEntry(int index, double value)	Set a single element.
void	setSubVector(int index, double[] v)	Set a set of consecutive elements.
void	setSubVector(int index, RealVector v)	Set a set of consecutive elements.
Iterator<RealVector.Entry>	sparseIterator()	Specialized implementations may choose to not iterate over all dimensions, either because those values are unset, or are equal to defaultValue(), or are small enough to be ignored for the purposes of iteration.
OpenMapRealVector	subtract(double[] v)	Subtract v from this vector.
OpenMapRealVector	subtract(OpenMapRealVector v)	Optimized method to subtract OpenMapRealVectors.
OpenMapRealVector	subtract(RealVector v)	Subtract v from this vector.
double[]	toArray()	Convert the vector to a double array.
void	unitize()	Converts this vector into a unit vector.
OpenMapRealVector	unitVector()	Creates a unit vector pointing in the direction of this vector.

Methods inherited from class org.apache.commons.math.linear.AbstractRealVector

add, dotProduct, getL1Norm, getLInfNorm, getMaxIndex, getMaxValue, getMinIndex, getMinValue, getNorm, iterator, map, mapAbs, mapAbsToSelf, mapAcos, mapAcosToSelf, mapAsin, mapAsinToSelf, mapAtan, mapAtanToSelf, mapCbrt, mapCbrtToSelf, mapCeil, mapCeilToSelf, mapCos, mapCosh, mapCoshToSelf, mapCosToSelf, mapDivide, mapDivideToSelf, mapExp, mapExpm1, mapExpm1ToSelf, mapExpToSelf, mapFloor, mapFloorToSelf, mapInv, mapInvToSelf, mapLog, mapLog10, mapLog10ToSelf, mapLog1p, mapLog1pToSelf, mapLogToSelf, mapMultiply, mapMultiplyToSelf, mapPow, mapPowToSelf, mapRint, mapRintToSelf, mapSignum, mapSignumToSelf, mapSin, mapSinh, mapSinhToSelf, mapSinToSelf, mapSqrt, mapSqrtToSelf, mapSubtract, mapSubtractToSelf, mapTan, mapTanh, mapTanhToSelf, mapTanToSelf, mapToSelf, mapUlp, mapUlpToSelf, outerProduct

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.apache.commons.math.linear.RealVector

add, dotProduct, getL1Norm, getLInfNorm, getNorm, iterator, map, mapAbs, mapAbsToSelf, mapAcos, mapAcosToSelf, mapAsin, mapAsinToSelf, mapAtan, mapAtanToSelf, mapCbrt, mapCbrtToSelf, mapCeil, mapCeilToSelf, mapCos, mapCosh, mapCoshToSelf, mapCosToSelf, mapDivide, mapDivideToSelf, mapExp, mapExpm1, mapExpm1ToSelf, mapExpToSelf, mapFloor, mapFloorToSelf, mapInv, mapInvToSelf, mapLog, mapLog10, mapLog10ToSelf, mapLog1p, mapLog1pToSelf, mapLogToSelf, mapMultiply, mapMultiplyToSelf, mapPow, mapPowToSelf, mapRint, mapRintToSelf, mapSignum, mapSignumToSelf, mapSin, mapSinh, mapSinhToSelf, mapSinToSelf, mapSqrt, mapSqrtToSelf, mapSubtract, mapSubtractToSelf, mapTan, mapTanh, mapTanhToSelf, mapTanToSelf, mapToSelf, mapUlp, mapUlpToSelf, outerProduct

Field Details

DEFAULT_ZERO_TOLERANCE

public static final double DEFAULT_ZERO_TOLERANCE

Default Tolerance for having a value considered zero.

See Also:

• Constant Field Values

Constructor Details

OpenMapRealVector

public OpenMapRealVector()

Build a 0-length vector.

Zero-length vectors may be used to initialized construction of vectors by data gathering. We start with zero-length and use either the OpenMapRealVector(OpenMapRealVector, int) constructor or one of the append method (append(double), append(double[]), append(RealVector)) to gather data into this vector.

OpenMapRealVector

public OpenMapRealVector(int dimension)

Construct a (dimension)-length vector of zeros.

Parameters:

dimension - size of the vector

OpenMapRealVector

public OpenMapRealVector(int dimension,
 double epsilon)

Construct a (dimension)-length vector of zeros, specifying zero tolerance.

Parameters:

dimension - Size of the vector

epsilon - The tolerance for having a value considered zero

OpenMapRealVector

public OpenMapRealVector(int dimension,
 int expectedSize)

Build a vector with known the sparseness (for advanced use only).

Parameters:

dimension - The size of the vector

expectedSize - The expected number of non-zero entries

OpenMapRealVector

public OpenMapRealVector(int dimension,
 int expectedSize,
 double epsilon)

Build a vector with known the sparseness and zero tolerance setting (for advanced use only).

Parameters:

dimension - The size of the vector

expectedSize - The expected number of non-zero entries

epsilon - The tolerance for having a value considered zero

OpenMapRealVector

public OpenMapRealVector(double[] values)

Create from a double array. Only non-zero entries will be stored

Parameters:

values - The set of values to create from

OpenMapRealVector

public OpenMapRealVector(double[] values,
 double epsilon)

Create from a double array, specifying zero tolerance. Only non-zero entries will be stored

Parameters:

values - The set of values to create from

epsilon - The tolerance for having a value considered zero

OpenMapRealVector

public OpenMapRealVector(Double[] values)

Create from a Double array. Only non-zero entries will be stored

Parameters:

values - The set of values to create from

OpenMapRealVector

public OpenMapRealVector(Double[] values,
 double epsilon)

Create from a Double array. Only non-zero entries will be stored

Parameters:

values - The set of values to create from

epsilon - The tolerance for having a value considered zero

OpenMapRealVector

public OpenMapRealVector(OpenMapRealVector v)

Copy constructor.

Parameters:

v - The instance to copy from

OpenMapRealVector

public OpenMapRealVector(RealVector v)

Generic copy constructor.

Parameters:

v - The instance to copy from

Method Details

add

public RealVector add(RealVector v)
               throws IllegalArgumentException

Compute the sum of this vector and v.

Specified by:

add in interface RealVector

Overrides:

add in class AbstractRealVector

Parameters:

v - Vector to be added.

Returns:

this + v.

Throws:

IllegalArgumentException

add

public OpenMapRealVector add(OpenMapRealVector v)
                      throws IllegalArgumentException

Optimized method to add two OpenMapRealVectors. Copies the larger vector, iterates over the smaller.

Parameters:

v - Vector to add with

Returns:

The sum of this with v

Throws:

IllegalArgumentException - If the dimensions don't match

append

public OpenMapRealVector append(OpenMapRealVector v)

Optimized method to append a OpenMapRealVector.

Parameters:

v - vector to append

Returns:

The result of appending v to self

append

public OpenMapRealVector append(RealVector v)

Construct a vector by appending a vector to this vector.

Specified by:

append in interface RealVector

Parameters:

v - vector to append to this one.

Returns:

a new vector

append

public OpenMapRealVector append(double d)

Construct a vector by appending a double to this vector.

Specified by:

append in interface RealVector

Parameters:

d - double to append.

Returns:

a new vector

append

public OpenMapRealVector append(double[] a)

Construct a vector by appending a double array to this vector.

Specified by:

append in interface RealVector

Parameters:

a - double array to append.

Returns:

a new vector

copy

public OpenMapRealVector copy()

Returns a (deep) copy of this vector.

Specified by:

copy in interface RealVector

Specified by:

copy in class AbstractRealVector

Returns:

a vector copy.

Since:

2.1

dotProduct

public double dotProduct(OpenMapRealVector v)
                  throws IllegalArgumentException

Optimized method to compute the dot product with an OpenMapRealVector. Iterates over the smaller of the two.

Parameters:

v - The vector to compute the dot product with

Returns:

The dot product of this and v

Throws:

IllegalArgumentException - If the dimensions don't match

dotProduct

public double dotProduct(RealVector v)
                  throws IllegalArgumentException

Compute the dot product.

Specified by:

dotProduct in interface RealVector

Overrides:

dotProduct in class AbstractRealVector

Parameters:

v - vector with which dot product should be computed

Returns:

the scalar dot product between instance and v

Throws:

IllegalArgumentException

ebeDivide

public OpenMapRealVector ebeDivide(RealVector v)
                            throws IllegalArgumentException

Element-by-element division.

Specified by:

ebeDivide in interface RealVector

Parameters:

v - vector by which instance elements must be divided

Returns:

a vector containing this[i] / v[i] for all i

Throws:

IllegalArgumentException

ebeDivide

public OpenMapRealVector ebeDivide(double[] v)
                            throws IllegalArgumentException

Element-by-element division.

Specified by:

ebeDivide in interface RealVector

Overrides:

ebeDivide in class AbstractRealVector

Parameters:

v - vector by which instance elements must be divided

Returns:

a vector containing this[i] / v[i] for all i

Throws:

IllegalArgumentException

ebeMultiply

public OpenMapRealVector ebeMultiply(RealVector v)
                              throws IllegalArgumentException

Element-by-element multiplication.

Specified by:

ebeMultiply in interface RealVector

Parameters:

v - vector by which instance elements must be multiplied

Returns:

a vector containing this[i] * v[i] for all i

Throws:

IllegalArgumentException

ebeMultiply

public OpenMapRealVector ebeMultiply(double[] v)
                              throws IllegalArgumentException

Element-by-element multiplication.

Specified by:

ebeMultiply in interface RealVector

Overrides:

ebeMultiply in class AbstractRealVector

Parameters:

v - vector by which instance elements must be multiplied

Returns:

a vector containing this[i] * v[i] for all i

Throws:

IllegalArgumentException

getSubVector

public OpenMapRealVector getSubVector(int index,
 int n)
                               throws MatrixIndexException

Get a subvector from consecutive elements.

Specified by:

getSubVector in interface RealVector

Parameters:

index - index of first element.

n - number of elements to be retrieved.

Returns:

a vector containing n elements.

Throws:

MatrixIndexException

getData

public double[] getData()

Returns vector entries as a double array.

Specified by:

getData in interface RealVector

Overrides:

getData in class AbstractRealVector

Returns:

double array of entries

getDimension

public int getDimension()

Returns the size of the vector.

Specified by:

getDimension in interface RealVector

Returns:

size

getDistance

public double getDistance(OpenMapRealVector v)
                   throws IllegalArgumentException

Optimized method to compute distance.

Parameters:

v - The vector to compute distance to

Returns:

The distance from this and v

Throws:

IllegalArgumentException - If the dimensions don't match

getDistance

public double getDistance(RealVector v)
                   throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with the L₂ norm, i.e. the square root of the sum of elements differences, or euclidian distance.

Specified by:

getDistance in interface RealVector

Overrides:

getDistance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getL1Distance(RealVector)
• RealVector.getLInfDistance(RealVector)
• RealVector.getNorm()

getDistance

public double getDistance(double[] v)
                   throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with the L₂ norm, i.e. the square root of the sum of elements differences, or euclidian distance.

Specified by:

getDistance in interface RealVector

Overrides:

getDistance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getL1Distance(double[])
• RealVector.getLInfDistance(double[])
• RealVector.getNorm()

getEntry

public double getEntry(int index)
                throws MatrixIndexException

Returns the entry in the specified index.

Specified by:

getEntry in interface RealVector

Parameters:

index - Index location of entry to be fetched.

Returns:

the vector entry at index.

Throws:

MatrixIndexException

See Also:

• RealVector.setEntry(int, double)

getL1Distance

public double getL1Distance(OpenMapRealVector v)

Distance between two vectors.

This method computes the distance consistent with L₁ norm, i.e. the sum of the absolute values of elements differences.

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

getL1Distance

public double getL1Distance(RealVector v)
                     throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with L₁ norm, i.e. the sum of the absolute values of elements differences.

Specified by:

getL1Distance in interface RealVector

Overrides:

getL1Distance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getDistance(RealVector)
• RealVector.getLInfDistance(RealVector)
• RealVector.getL1Norm()

getL1Distance

public double getL1Distance(double[] v)
                     throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with L₁ norm, i.e. the sum of the absolute values of elements differences.

Specified by:

getL1Distance in interface RealVector

Overrides:

getL1Distance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getDistance(double[])
• RealVector.getLInfDistance(double[])
• RealVector.getL1Norm()

getLInfDistance

public double getLInfDistance(RealVector v)
                       throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with L_∞ norm, i.e. the max of the absolute values of elements differences.

Specified by:

getLInfDistance in interface RealVector

Overrides:

getLInfDistance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getDistance(RealVector)
• RealVector.getL1Distance(RealVector)
• RealVector.getLInfNorm()

getLInfDistance

public double getLInfDistance(double[] v)
                       throws IllegalArgumentException

Distance between two vectors.

This method computes the distance consistent with L_∞ norm, i.e. the max of the absolute values of elements differences.

Specified by:

getLInfDistance in interface RealVector

Overrides:

getLInfDistance in class AbstractRealVector

Parameters:

v - vector to which distance is requested

Returns:

distance between two vectors.

Throws:

IllegalArgumentException

See Also:

• RealVector.getDistance(double[])
• RealVector.getL1Distance(double[])
• RealVector.getLInfNorm()

isInfinite

public boolean isInfinite()

Check whether any coordinate of this vector is infinite and none are NaN.

Specified by:

isInfinite in interface RealVector

Returns:

true if any coordinate of this vector is infinite and none are NaN, false otherwise.

isNaN

public boolean isNaN()

Check whether any coordinate of this vector is NaN.

Specified by:

isNaN in interface RealVector

Returns:

true if any coordinate of this vector is NaN, false otherwise.

mapAdd

public OpenMapRealVector mapAdd(double d)

Add a value to each entry.

Specified by:

mapAdd in interface RealVector

Overrides:

mapAdd in class AbstractRealVector

Parameters:

d - Value to be added to each entry.

Returns:

this + d.

mapAddToSelf

public OpenMapRealVector mapAddToSelf(double d)

Add a value to each entry. The instance is changed in-place.

Specified by:

mapAddToSelf in interface RealVector

Overrides:

mapAddToSelf in class AbstractRealVector

Parameters:

d - Value to be added to each entry.

Returns:

this.

outerProduct

public RealMatrix outerProduct(double[] v)
                        throws IllegalArgumentException

Compute the outer product.

Specified by:

outerProduct in interface RealVector

Overrides:

outerProduct in class AbstractRealVector

Parameters:

v - vector with which outer product should be computed

Returns:

the square matrix outer product between instance and v

Throws:

IllegalArgumentException

projection

public RealVector projection(RealVector v)
                      throws IllegalArgumentException

Find the orthogonal projection of this vector onto another vector.

Specified by:

projection in interface RealVector

Parameters:

v - vector onto which instance must be projected

Returns:

projection of the instance onto v

Throws:

IllegalArgumentException

projection

public OpenMapRealVector projection(double[] v)
                             throws IllegalArgumentException

Find the orthogonal projection of this vector onto another vector.

Specified by:

projection in interface RealVector

Overrides:

projection in class AbstractRealVector

Parameters:

v - vector onto which instance must be projected

Returns:

projection of the instance onto v

Throws:

IllegalArgumentException

setEntry

public void setEntry(int index,
 double value)
              throws MatrixIndexException

Set a single element.

Specified by:

setEntry in interface RealVector

Parameters:

index - element index.

value - new value for the element.

Throws:

MatrixIndexException

See Also:

• RealVector.getEntry(int)

setSubVector

public void setSubVector(int index,
 RealVector v)
                  throws MatrixIndexException

Set a set of consecutive elements.

Specified by:

setSubVector in interface RealVector

Overrides:

setSubVector in class AbstractRealVector

Parameters:

index - index of first element to be set.

v - vector containing the values to set.

Throws:

MatrixIndexException

See Also:

• RealVector.setSubVector(int, double[])

setSubVector

public void setSubVector(int index,
 double[] v)
                  throws MatrixIndexException

Set a set of consecutive elements.

Specified by:

setSubVector in interface RealVector

Overrides:

setSubVector in class AbstractRealVector

Parameters:

index - index of first element to be set.

v - vector containing the values to set.

Throws:

MatrixIndexException

See Also:

• RealVector.setSubVector(int, RealVector)

set

public void set(double value)

Set all elements to a single value.

Specified by:

set in interface RealVector

Overrides:

set in class AbstractRealVector

Parameters:

value - single value to set for all elements

subtract

public OpenMapRealVector subtract(OpenMapRealVector v)
                           throws IllegalArgumentException

Optimized method to subtract OpenMapRealVectors.

Parameters:

v - The vector to subtract from this

Returns:

The difference of this and v

Throws:

IllegalArgumentException - If the dimensions don't match

subtract

public OpenMapRealVector subtract(RealVector v)
                           throws IllegalArgumentException

Subtract v from this vector.

Specified by:

subtract in interface RealVector

Overrides:

subtract in class AbstractRealVector

Parameters:

v - Vector to be subtracted.

Returns:

this - v.

Throws:

IllegalArgumentException

subtract

public OpenMapRealVector subtract(double[] v)
                           throws IllegalArgumentException

Subtract v from this vector.

Specified by:

subtract in interface RealVector

Overrides:

subtract in class AbstractRealVector

Parameters:

v - Vector to be subtracted.

Returns:

this - v.

Throws:

IllegalArgumentException

unitVector

public OpenMapRealVector unitVector()

Creates a unit vector pointing in the direction of this vector.

The instance is not changed by this method.

Specified by:

unitVector in interface RealVector

Overrides:

unitVector in class AbstractRealVector

Returns:

a unit vector pointing in direction of this vector

unitize

public void unitize()

Converts this vector into a unit vector.

The instance itself is changed by this method.

Specified by:

unitize in interface RealVector

Overrides:

unitize in class AbstractRealVector

toArray

public double[] toArray()

Convert the vector to a double array.

The array is independent from vector data, it's elements are copied.

Specified by:

toArray in interface RealVector

Overrides:

toArray in class AbstractRealVector

Returns:

array containing a copy of vector elements

hashCode

public int hashCode()

Implementation Note: This works on exact values, and as a result it is possible for a.subtract(b) to be the zero vector, while a.hashCode() != b.hashCode().

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Implementation Note: This performs an exact comparison, and as a result it is possible for a.subtract(b} to be the zero vector, while a.equals(b) == false.

Overrides:

equals in class Object

getSparcity

@Deprecated
public double getSparcity()

Deprecated.

as of 2.2 replaced by the correctly spelled getSparsity()

Returns:

the percentage of none zero elements as a decimal percent.

getSparsity

public double getSparsity()

Returns:

the percentage of none zero elements as a decimal percent.

Since:

2.2

sparseIterator

public Iterator<RealVector.Entry> sparseIterator()

Specialized implementations may choose to not iterate over all dimensions, either because those values are unset, or are equal to defaultValue(), or are small enough to be ignored for the purposes of iteration. No guarantees are made about order of iteration. In dense implementations, this method will often delegate to RealVector.iterator().

Specified by:

sparseIterator in interface RealVector

Overrides:

sparseIterator in class AbstractRealVector

Returns:

a sparse iterator